DESCRIPTION: (from the abstract) This application is for continuation support of an ongoing prospective randomized clinical trial (RCT) examining the effectiveness, costs and benefits of two general strategies that are prevalent today for the timing of treatment of Class II malocclusions. The first, a dual phase treatment, calls for intervention during the preadolescent years (ages 8-11) with limited goals that include correction of the molar distocclusion, improvement of the overjet/overbite relationships and incisor alignment, usually followed by a more definitive intervention during adolescence (ages 12-15) designed to finish and detail the result. The second strategy, a single phase treatment, accomplishes the entire correction during the adolescent years. The relative effectiveness of the two approaches to Class II treatment have not been compared, especially in the long-term. The effect on the dental outcome, the esthetic outcome, the periodontal tissues, the temporomandibular joint or the psychosocial effect on the subjects in the long-term have never been examined. Whether initial severity of the malocclusion influences the outcome is also unclear. In addition, the benefits and the risks of these two strategies are not well understood. Clinicians treat using one approach or the other, based more on office convenience or personal biases than on clinical evidence. This research will provide the practicing clinician information to appropriately advise the parents of prospective patients concerning either approach. During the initial funding period (Phase 1 of the RCT), methods were implemented to compare early treatment with bionators and headgears, with and without retention, to no early treatment in the broadest possible way to produce data on effectiveness and relative cost (risk) and benefit. During the second funding period, the second phase of definite orthodontic treatment was completed on the early-treated subjects as well as the control subjects. This application for the 3rd phase of the RCT will demonstrate the considerable progress already made toward achieving current aims and provide evidence that methods/subjects are in place after 9 years to ensure completion of Phase 2 of the RCT and justify continuation for a 3rd funding period. This continuation application proposes three additional specific aims: 1. Compare stability and long-term treatment affects on the oral health of subjects receiving single phase versus dual phase correction of Class II malocclusion. 2. Compare oral health status and attitudes towards dental health, orthodontics, and concepts of self-image between subjects who participated in the Class II RCT with those who qualified and did not participate. 3. Develop predictive and mechanistic multivariate models to evaluate the effectiveness of single versus dual phase correction of Class II malocclusion using multivariate regression models, fuzzy analysis, and cost-effectiveness analysis.